Crystals called COP-free crystals as kinds of wafer products are being increasingly used. This COP-free region (N-region) is a portion which does not include a huge dislocation cluster (I-region), COP (V-region), a defect detectable by Cu deposition, or an oxidation induced stacking fault (OSF) region.
Checking the huge dislocation cluster by etching called LEP in a crystal inspection process, and an Enhanced-OSF (EOSF) inspection are given as methods of guarantee this (See Patent Documents 1 and 2), and identification can be made by these methods.
Production of a silicon single crystal ingot composed of an N-region by the CZ method can be achieved when the ingot is produced at a given growth rate under conditions that maintain a constant temperature gradient near the growth interface in its plane. It is required that F/G be in the range that allows the N-region to be formed on the entire plane, where G is the temperature gradient of a crystal near the growth interface and F is the growth rate (pulling rate) of the crystal. Such a range is narrow. If F or G exceeds the desired requested range, then no N-region is formed, resulting in a failure product.
Thus, this product has a narrow production margin. It is necessary to always monitor which defect region among the V-region, the OSF region, the N-region (Nv-region or Ni-region), and the I-region the production is made with. If necessary, the tuning (adjustment) of pulling conditions is needed. The reason is that since a temperature distribution in a furnace varies over time due to a variation of furnace components to be used, such as heater, insulation, and other components, with time, the tuning of the pulling conditions is essential to stably produce an N-region crystal.